On Thursday NASA administrator Charles Bolden reassured lawmakers that Russia won’t stop providing access for US astronauts to the International Space Station, despite the current tensions between the two countries over Russia’s recent invasion of Crimea.

In testimony before the House Science, Space, and Technology Committee, Bolden said that Russia relies on the US to operate major systems aboard the ISS, so it would not cancel its contract with NASA to ferry astronauts to and from the station on Soyuz capsules. The ISS, he said, “would probably have to shut down if Russia denies us access. They can’t operate it without us.” The US provides the power and other “everyday operations” on the ISS, he said, adding that Russia is “equally worried about the US terminating operations” on the ISS.

Bolden noted that the agreement, for which the US pays $70 million per astronaut, is with the Russian Space Agency, and that NASA’s relations with the RSA had been unaffected by Russia’s war with Georgia in 2008, when the US condemned Russia’s incursion there. NASA has depended on Russia for crew transportation since the space shuttle was retired in 2011. Pressed by several lawmakers, Bolden said the need for maintenance and repairs would preclude the ISS from sitting unoccupied in orbit.

The NASA chief also said he has “high confidence” that a US-based crew transport will be ready to fly in 2017, but only if Congress appropriates the full $848.3 million that the agency has requested for its commercial crew vehicle program in fiscal year 2015. NASA is funding three companies—Space X, Sierra Nevada, and Boeing—to develop separate designs for a low-Earth-orbit crew vehicle. Bolden said that the 2017 launch date could be moved up by as much as one year if more funding was made available to the program. Insufficient funding in past years caused the schedule to slip from its original 2015 date.